1. Field of the Invention
This invention relates generally to smoothing circuits and is directed to improvements in a smoothing circuit for a display apparatus.
2. Description of the Prior Art
For transmitting information, such as news, weather forecasts, announcements or the like through the use of a telephone network or the vertical blanking period of a television broadcast, it is known to use various systems, such as, a so-called CAPTAIN (Character And Pattern Telephone Access Information Network) system, a multiplex character television broadcast and so on.
In such transmitting systems, the transmitting section converts characters, such as letters, numerals or symbols, into code signals and transmits the same, while the receiving section decodes the original characters from the received code signals and displays the same on a picture screen of a television receiver.
By way of example, in the case of the letter "A", a code signal "41" (hexadecimal code) indicating the letter "A" is converted into a binary coded signal of 8 bits for each numeral and then transmitted by the transmitting section. In the receiving section this coded signal "41" is supplied to a character memory (character generator), in which is formed a luminance signal, which will form a pattern of the letter "A" and therefore the letter "A" is displayed on the picture screen of the television receiver. Further, in the prior art, smoothing is effected to make the displayed character easy to see.
For example, FIG. 1 schematically illustrates an original pattern of the character or letter "A" as written in the character memory. This original pattern is composed of, for example, a dot matrix system consisting of 5.times.7 dots. FIG. 2 schematically illustrates the character "A" of FIG. 1 as displayed on the picture screen of the television receiver, in the case where smoothing has not been effected. Reference letters L.sub.1 to L.sub.14 (L.sub.2m+1, L.sub.2m, . . . m is an integer including 0) denote scanning lines, with the scanning lines shown by broken lines being formed during each odd-numbered field, while the scanning lines shown by solid lines are formed during each even-numbered field. Moreover, reference letter Du generally identifies a dot (luminance point) of standard or fundamental size, and since the output (FIG. 1) of the character memory is utilized in both the odd- and even-numbered fields, the displayed pattern is as shown in FIG. 2.
When smoothing is conducted according to the prior art, the letter "A" is displayed on the picture screen of the television receiver as shown in FIG. 3, and in which half dots Dh, each having a width one-half that of the initial or fundamental dot Du, are added to the display pattern shown in FIG. 2. Accordingly, the displayed letter "A" in FIG. 3 is smoother than the displayed letter "A" in FIG. 2, and becomes easier to recognize. For this smoothing according to the prior art, there are only two basic combinations of the half dot Dh with the standard or fundamental dot Du as shown in FIG. 4. In other words, for all characters, the half dots D.sub.h are added to the respective standard dots Du only on the basis of the combinations shown in FIG. 4.
When smoothing is conducted by adding the half dots Dh only on the basis of the two combinations shown in FIG. 4, if the original patterns are, for example, the characters shown in FIG. 5, the resulting displayed patterns become those shown in FIG. 6. It will be appreciated therefrom that, when the oblique line portion of the displayed pattern is very steep as in the letter "V" at the top of FIG. 5, the smoothness of such portion leaves much to be desired. In the case of an oblique line portion as in the symbol or slash "/" in the middle portion of FIG. 5, smoothing according to the prior art increases the boldness of that symbol more than is required for good recognition. Finally, in the case of the symbol " " shown at the bottom of FIG. 5, the central open portion corresponding in size to a standard dot Du is filled with half dots Dh as a result of the smoothing according to the prior art, as shown at the bottom of FIG. 6.